Various methods have been proposed to polish the fine irregularity on a metal surface (http://www.chemicoat.co.jp/column/detail_6.html).
“Chemical polishing” denotes a polishing technique that soaks a metal in a solution for polishing, in order to corrode the surface of the metal by chemical reaction of an acid or an alkali. The solution enters even a small part to process the small part, which is not processible by mechanical polishing. Chemical polishing is mainly suitable to polish a micro-component of a complicated shape or an internal surface.
“Electrolytic polishing” denotes a polishing technique that soaks a metal in a solution for electrolytic polishing and polishes the metal as the positive electrode in the solution by the flow of electric current. The metal is gradually electrolyzed to give a gloss or a smooth surface. This technique does not make any altered layer on the surface by processing and does not leave any stain or burn. Electrolytic polishing as well as chemical polishing is used for, for example, precision components that require a clean polishing technique.
“Mechanical Polishing” denotes a polishing technique using a machine and includes various methods. A rotary polishing technique is a currently dominant technique that applies a polishing pad on a disk-shaped surface plate, drops down a liquid polishing agent including a chemical component and fine particles on the polishing pad, and polishes the surface with the rotating polishing pad. Other polishing techniques include a method of precisely polishing an inner diameter of a metal with a honing machine and buffing using a buff.
Satin finish (http://www.chemicoat.co.jp/knowledge/detail_169.htmol) is a surface treatment method that forms fine concaves and convexes on the surface of a metal to provide rough texture. Satin finish is also called pear-skin finish, since the finished surface is similar to the surface of a fruit, pear. Satin finish includes gloss finish, semi-gloss finish and matte finish. Satin finish is employed for the purpose of improving the texture and the appearance, for the purpose of anti-slip to help the grasp of an oily hand, and for the purpose of pretreatment of coating or anodization. “Manual scraping” may be employed to form fine concaves and convexes, in order to reduce the friction resistance of the metal surface of, for example, a precision machine.
Satin finish of the metal surface mainly includes mechanical methods and chemical methods. The mechanical methods include a wire brushing method that polishes the metal surface with a wire brush, a sand blast method that sprays fine particles against the surface by the compressed air, and a liquid honing method that sprays a processing solution including fine particles onto a target surface of metal processing, in addition to the manual scraping described above. The chemical methods of satin finish include a method of chemical corrosion or galvanic corrosion such as etching and a surface treatment method using electroplating such as dispersal plating.
Roughness meters are generally used for measurement of the surface gloss or roughness. The roughness meters include mechanical types and optical types using, for example, laser. The roughness meter provides a numerical indication of the irregularity in the unit of millimeter or in the unit of nanometer. A skilled worker in the field evaluates the surface condition by visually checking the gloss and the shine of the surface, rather than the numerical measurement. The work generally proceeds, based on the result of evaluation by the skilled worker in the field.